1. Field of the Invention
This invention relates to the field of implantable medical devices, such as stents. More particularly, this invention is directed to coatings for devices, the coatings including peptides such as polymers and/or oligomers of L-arginine.
2. Description of the Background
In the field of medical technology, there is frequently a necessity to administer a therapeutic substance locally. To provide an efficacious concentration to the treatment site, systemic administration of medication often produces adverse or toxic side effect for the patient. Local delivery is a preferred method in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Thus, local delivery produces fewer side effects and achieves more effective results. For the treatment of vascular occlusions, such as restenosis, stents are being modified to administer therapeutic substances locally. One method of medicating a stent is with the use of a polymer coating impregnated with a therapeutic substance. The coating allows for the sustained release of the substance at the treatment site. L-arginine, or polypeptide oligomeric derivatives or analogs thereof, for example, those containing 5 to 20 amino acid units are one example of a therapeutic substance that can be used in conjunction with a stent.
L-arginine is a known precursor of endothelium derived nitric oxide (NO). NO is synthesized from L-arginine, or its polymeric and/or oligomeric derivatives, by the enzyme NO synthase oxygenase, a homodimeric flavo-hemoprotein that catalyzes the 5-electron oxidation of L-arginine to produce NO and L-citrulline. Among other therapeutic properties, NO regulates vascular tone, inhibits platelet aggregation, and inhibits vascular smooth muscle proliferation. These therapeutic properties are believed to contribute to the reduction or elimination of neo-intimal hyperplasia in vascular injury models.
U.S. Pat. No. 5,861,168 to Cooke et al. teaches that NO activity is reduced after vascular injury. Cooke et al. also teach that administering L-arginine as the NO precursor helps to restore vascular NO activity in patients with endothelial vasodilator dysfunction due to restenosis. It has been also taught that oligomeric peptides comprising 6 to 15 units of L- or D-arginine can be effective transfectors of cells (see, Mitchell, et al., J. Peptide Res., vol. 56, p. 318 (2000)) and, using a rabbit vein-graft model, it has been demonstrated that oligomers of L- or D-arginine can inhibit vascular smooth cell proliferation by efficiently transfecting cells. See, Uemura, et al., Circulation, vol. 102, p. 2629 (2000). Using the rabbit model, it has also been shown that intramural administration of L-arginine inhibits lesion formation in a hypercholesterolemic balloon injury. See, Schwarzacher et al. Circulation, vol. 95, p. 1863 (1997).
Accordingly, it is desirable to incorporate L-arginine, or its polymers and/or oligomers into a stent coating. The present application describes the methods that can be used to achieve this goal.